JPH0221787Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a tone control circuit, and an object of the present invention is to provide a tone control that can simultaneously enhance or attenuate a high frequency band and a low frequency band using a single variable resistor. .

In conventional tone control circuits, when adjusting the low and high frequency bands within the audible frequency band, separate variable resistance elements are operated to vary the frequency characteristics of the low and high frequencies. The conventional method was to perform tone control using the frequency band, or to subdivide the frequency band into multiple bands and control the frequency characteristics of each band using a variable resistance element corresponding to each divided band. The frequency characteristics of only one band could be varied using the variable resistance element.

Furthermore, when using the above tone control circuit in audio equipment that uses small speakers such as radio cassettes, since the reproduction ability of the small speaker in the low frequency band is inferior, changing the high frequency will improve the balance with the low frequency band. tended to be lost.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of an embodiment of the tone control circuit according to the present invention. In the same figure, input terminal 1
is connected to output terminal 2 via resistor R ₁ , while
It is connected to fixed terminal a of variable resistor VR via capacitor _C1 . The variable resistor VR has its fixed terminal b connected to the output terminal 2, while its slider is connected to the output terminal ₂ via the capacitor C2,
And it is grounded via resistor _R2 . In addition,
As an example, capacitor _C1 is 6800pF, _C2 is 0.1μF,
Resistor R ₁ is selected to be 12 kΩ, R ₂ to 2.2 kΩ, and the maximum resistance value R _x of variable resistor VR is selected to be 50 kΩ.

First, the operation when the slider of the variable resistor VR is slid all the way to the fixed terminal a side will be described.
In this case, the resistance value between the fixed terminal b of the variable resistor VR and the slider becomes the maximum value R _x , and the circuit shown in Figure 1 is equivalent to the one shown in Figure 2 A for low frequencies. It can be expressed by a circuit, and for high frequencies, it can be expressed by an equivalent circuit shown in FIG. 3A.

In other words, the capacitance value of capacitor C ₁ shown in Fig. 1 is, for example, 6800 pF, and the capacitance value of capacitor C ₂ is selected to be 0.1 μF, which is about 14.7 times larger than the capacitance value of C ₁ . On the other hand, the impedance of capacitor C ₁ becomes extremely large,
Since the impedance of capacitor _C2 is not negligible in a certain frequency range while C1 can be ignored, the circuit _shown in FIG. 1 can be represented by an equivalent circuit as shown in FIG. 2A. The amplitude-frequency characteristics of the equivalent circuit shown in FIG. 2A exhibit low-frequency enhancement and high-frequency attenuation characteristics.

Here, the equivalent circuit shown in Figure 2A is
In the middle frequency band higher than _{the frequency L expressed} by R ₂ + R _x /2πC ₂・R ₂・R
The impedance of capacitor C ₂ in the equivalent circuit shown in Figure A becomes extremely small and can be considered as having both ends of resistor R _x shorted, so in the end, in this mid-range frequency band, the impedance is 20log (R ₂ /R ₁ +R ₂ ) [ It exhibits flat characteristics with a gain of (dB).

On the other hand, the equivalent circuit shown in FIG. 2A has the above frequency _L
In the frequency band up to a certain frequency ₁ lower than
It exhibits an attenuation characteristic of 6 dB/octave, but in a frequency band even lower than frequency ₁ , its impedance becomes so large that the capacitor C ₂ in the equivalent circuit shown in FIG. 2A can be ignored. For this reason, the frequency
In a frequency band even lower than ₁ , the tone control circuit shown in Figure 1 is equivalent to the equivalent circuit shown in Figure 2A, ignoring the capacitor _C2 ,
Therefore, the amplitude-frequency characteristic in this extremely low frequency band is flat, and the gain is 20log.
(R _x + R ₂ / R ₁ + R _x + R ₂ ) It can be expressed in [dB].

From the above, the slider of variable resistor VR is fixed to terminal a.
The amplitude-frequency characteristic of the tone control circuit shown in FIG. 1 with respect to low frequencies when the tone control circuit is slid all the way to the end is as shown in FIG. 2B.

Next, we will explain the amplitude-frequency characteristics for high frequencies of the tone control circuit shown in Figure 1 when the slider of the variable resistor VR is slid all the way to the fixed terminal a side.
The impedance of C ₂ is extremely small, and the impedance of capacitor C ₁ is relatively large below a certain frequency. Therefore, the tone control circuit shown in FIG. 1 can be constructed by shortening the entire resistance from the fixed terminals a to b of the variable resistor VR by the capacitor _C2 , so the equivalent circuit as shown in FIG. 3A is obtained. It can be expressed as

The amplitude-frequency characteristic of the equivalent circuit shown in Figure 3A is flat at frequencies below frequency _H , which can be expressed as 1/2πC ₁ R ₁ , and from frequency _H to R ₁ +R ₂ /2πC ₁ (R ₁ +R ₂ ). It increases at a rate of 6 dB/octave towards frequency ₂ , and becomes flat at frequencies above that, exhibiting low-frequency attenuation and high-frequency enhancement characteristics. Therefore, in the middle frequency band lower than the above frequency _H , the impedance of capacitor C ₁ becomes extremely large, and since the capacitor C ₁ in the equivalent circuit shown in Figure 3A can be ignored, in the middle frequency band The gain becomes flat at 20log(R ₂ /R ₁ +R ₂ ) [dB]. On the other hand, in a frequency band higher than frequency ₂ , the impedance of capacitor _C1 becomes extremely small. Therefore, in a frequency band higher than frequency ₂ , the tone control circuit shown in FIG. 1 has a resistance of the equivalent circuit shown in FIG.
Since both ends of _R1 can be regarded as equivalent to a circuit in which both ends are shorted, the amplitude-frequency characteristic in this high frequency band exhibits a flat characteristic at a gain of 0 dB.

From the above, the slider of variable resistor VR is fixed to terminal a.
The amplitude-frequency characteristic of the tone control circuit shown in FIG. 1 with respect to high frequencies when the tone control circuit is slid all the way to the end is as shown in FIG. 3B.

Next, the amplitude-frequency characteristics of the circuit of the present invention shown in FIG. 1 when the slider of the variable resistor VR is slid all the way to the fixed terminal b side will be explained. In this case, both ends of the capacitor _C2 in the tone control circuit shown in FIG. 1 are shot, so the capacitor _C2 can be ignored.
Therefore, between input terminal 1 and output terminal 2, a series circuit consisting of capacitor C ₁ and resistor R _x and a resistor are connected.
A parallel circuit with R ₁ is connected. Here, since the resistance R _x is selected to have an extremely large value of 50 kΩ as described above, it can be ignored. Therefore, when the slider of the variable resistor VR is slid all the way to the fixed terminal b side, the circuit of the present invention shown in _FIG.
It can be considered equivalent to a circuit consisting of R ₂ .

Therefore, the amplitude-frequency characteristics of the circuit of the present invention are flat over the entire frequency band, and the gain is
The characteristic is expressed by 20log(R ₂ /R ₁ +R ₂ ) [dB] as shown by the solid line in FIG. 4B. However, in reality, amplifiers are connected before input terminal 1 and after output terminal 2, and the overall frequency characteristics of these amplifiers exhibit high-frequency attenuation and low-frequency attenuation characteristics. When the actuator is slid all the way to the fixed terminal b side, the amplitude-frequency characteristics of the circuit of the present invention shown in Fig. 1 are actually in an extremely high frequency band and an extremely low frequency band, as shown by the dashed line in Fig. 4 B. It is attenuated in each frequency band, and exhibits flat characteristics in other frequency bands.

From the above, the amplitude-frequency characteristics of the circuit of the present invention are as shown in FIG. In the figure, frequencies _L and _H are the same frequencies as _L shown in FIG. 2B and _H shown in FIG. 3B, respectively; for example, _L is about 755 Hz and _H is about 1.95 kHz. Further, 20log (R ₂ /R ₁ +R ₂ ) is about -16.2 dB, and 20 log (R _x +R ₂ /R ₁ +R _x +R ₂ ) is about -1.8 dB. In Fig. 5, the solid line indicates the amplitude - when the slider of the variable resistor VR is fully slid to the fixed terminal a side.
In terms of frequency characteristics, as the slider slides toward the fixed terminal b, the low frequency band and the high frequency band simultaneously attenuate. Then fix the slider to terminal b
When it is slid all the way to the side, the amplitude-frequency characteristics of the tone control circuit shown in FIG. 1 become as shown by the dashed line in FIG. 5.

Therefore, depending on the sliding position of the slider of the variable resistor VR, the amplitude-frequency characteristics of the tone control circuit of the present invention shown in FIG. As the slider is moved toward the fixed terminal a side, the low frequency band and the high frequency band are simultaneously enhanced. As it is moved, the lower frequency band and the higher frequency band exhibit characteristics of being simultaneously attenuated.

Note that the mid-range frequency around 1kHz is not subject to control, so it always shows a gain of 20log (R ₂ /R ₁ +R ₂ ) [dB] regardless of the sliding position of the variable resistor VR slider. Output does not change.

As described above, according to the tone control circuit of the present invention, the low frequency band and the high frequency band can be attenuated or enhanced simultaneously and continuously and in the same direction using a single variable resistor.
Therefore, when used in an audio device having a small speaker, it has the advantage of being able to control the low frequency band and the high frequency band in a well-balanced manner.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the circuit of the present invention;
2A and 2B are diagrams showing the equivalent circuit and amplitude-frequency characteristics for the low frequency of the circuit shown in FIG. 1 when the slider of the variable resistor is slid all the way to one fixed terminal side, respectively; Figures 3A and 3B are diagrams showing the equivalent circuit and amplitude-frequency characteristics of the circuit shown in Figure 1 for high frequencies when the slider of the variable resistor is slid all the way to one fixed terminal side, respectively; Figures 4A and 4B are diagrams showing the equivalent circuit and amplitude-frequency characteristics when the slider of the variable resistor is slid all the way to the other fixed terminal side, and Figure 5 is the amplitude-frequency characteristic of the circuit of the present invention. FIG. 3 is a diagram illustrating an example of how frequency characteristics change. 1...Input terminal, 2...Output terminal, R ₁ , R ₂ ...
...Resistor, C ₁ , C ₂ ... Capacitor, VR ... Variable resistor.

Claims (1)

[Claims for Utility Model Registration] A first resistor connected between an input terminal and an output terminal, a first capacitor whose one end is connected to the input terminal, and a first fixed terminal connected to the first a variable resistor connected to the other end of the capacitor and having a second fixed terminal connected to the output terminal; a second capacitor connected between the slider of the variable resistor and the output terminal; , a second resistor connected between the slider of the variable resistor and the ground, and when the slider of the variable resistor is located at the first fixed terminal, a low frequency On the other hand, the first capacitor exhibits an extremely large impedance compared to the second capacitor, to the extent that the first capacitor can be ignored, and the second capacitor exhibits an impedance that is negligible compared to the second capacitor.
The capacitance values of the first and second capacitors are selected so that the impedance of the capacitor exhibits an extremely small impedance that substantially shoots the variable resistor, and the slider of the variable resistor is When located at the second fixed terminal, the maximum resistance value of the variable resistor is set so that the series circuit of the first capacitor and the variable resistor can be ignored with respect to the first resistance. A tone control circuit whose resistance value is selected to be sufficiently larger than each resistance value of the second resistor.